killing specular reflections with polarizing filters
I was reminded of this effect while observing a razor blade painted black using darkfield EPI illumination.
Some paint had flaked off the blade, causing specular reflections.
Applying cross-polarization substantially eliminated them, while white plastic beside the blade was still bright.
Cross-polarization seemingly is more expedient and portable than most diffuse illumination schemes.
Circular polarization puts a quarter wave plate orientated at 45 degrees,
so that equal amounts of fast and slow waves are excited.
Less obviously, quarter wave plates in neutral gray circular polarizing filters want quarter wave over visible wavelengths,
but wave plates are quarter at one (green) wavelength, provoking elliptical, rather than circular, polarization for other wavelengths.
Circular polarization and mirrors
With linear polarization side facing mirror, looking thru it shows the reflected filter only moderately darker than other reflected.
With circular polarization side facing mirror, looking thru it shows the reflected filter substantially extinguishing its mirror reflection.
Using 2 separate filters with quarter wave plates facing the mirror gives substantially full extinction independent of rotation.
Since rotation does not matter, this extinction must result from mirror reversing circular polarization handedness.
A half wave plate also reverses circular polarization handedness.
Quarter wave plate and specular reflections - photomacrography.net
A De Senarmont
polarizer is just a fixed quarter wave plate over a rotatable linear polarizer
According to the McCRONE group, "The Senarmont compensator consists of an accurate
quarter plate oriented so that one of its vibration directions, usually the high index (slow direction),
is parallel to the polarizer vibration direction (not at usual 45 degrees for quarter compensator)."
This contradicts Molecular Expressions
Polarized Light Microscopy: The de Senarmont Compensator".
Quarter wave plate before analyzer or after polarizer
Waveplate below condenser reduces object image quality impact,
but Nikon analyzer A is a circular polarizing filter...
"Normally these compensators would sit above the objective,
but this leaves very little in the way of experimentation
due to the small slots for retardation plates on most polarizing scopes
[or none at all on biological scopes modified
for polarizing use],
and the quality of the material itself is of lesser importance
not being directly after your favourite objective; plastic retardation plates
or poor quality mica can deteriorate the image if placed above the objective
[in the retardation slot if fitted], it certainly does on my microscope."
- Nikon Optiphot Pol manual
- Senarmont Compensator
- Universal epi-illuminator
For Optiphot Universal epi-illuminator rotating polarizing slider
My EPI rotating polarizing slider is missing the ND / wave plate insert:
Nikon Optiphot ND Filter Slider for Rotating Polarizer Universal Epi Illuminator
eBay item 325064013162
For Metaphot sliders:
eBay item: 265160069244
Ordered 30 Nov 2021 for Optiphot vertical illuminator, but fits Metaphot head,
need 20mm filters.
2 Microscope 20mm Linear Polarizing Filters High Quality Specs & BONUS Included
eBay item 275280951982
See specifications included. Made in USA by a top optical manufacturer.
Fully Laminated - 0.8mm thick. Rigid - will not bend.
Its thickness provides rigidity for self-standing applications.
Note: Since many of our buyers after making an order and receiving our polarizing filters
begin farming to find microscope slides with polarizing capability we did the following:
We included in this set a polarizing crystal microscope slider.
This bonus is represented by an Acetaminophen, Orange G, Safranin O or Potassium Ferricyanide microscope slide. (ONE Slide)
Since we depend by our supplier capabilities unfortunately we don't know which crystal will be included in the set.
20mm - 140nm Quarter Wave Microscope Lambda Plate plus BONUS slide - See SPECS
eBay item 275419900377
Microscope Quarter Wave Compensator Plate Multi Layers - Polarizing Applications.
0.5mm thick (active layer 0.08mm) 140nm +/- 10nm Retardance Value.
We attached a detailed specification page showing all features, components
and fabrication technology. Please see second attached picture.
We included in this sale as a bonus - a crystal polarizing microscope slide
with a birefringent chemical available at the time of sale.
In this way you can check the quality of our product right after receiving it.
Note: In our store we have listed two types of Lambda retaining plates:
Group one: Laminated and Group two: Glass Mounted.
Even same type of item - Quarter Lambda, for example interferometric has same value as Glass mounted quarter Lambda plates,
visual some differences are noticed due to the technology used.
Laminated plates are manufactured via hot lamination and at the line of contact between active layer
and neutral protection layer there is a micrometric melted layer combining the last two.
Visual this brings a color surplus in laminated lenses.
In group two (full Lambda retaining plates) the effect is reversed but less noticeable.
(For laser applications and special scientific research glass mounted retaining plates are usually the chosen choice.)
Nikon ND32 slider for universal vertical illuminator
30mm high, 13.3mm thick, 98mm long, 27mm diameter holes;
ordered a pair of these, supposing filters inside mounts are <= 27mm o.d.
Prinz 28mm Circular Polarizer Filter
eBay item: 191124651760
Prinz 28mm Circular Polarizing Filters - 28mm threads
I actually have 840 of these filters left but am listing a lower number.
I have been in the photo industry and am now getting out. I had these filters made a while back
for the Nikon Coolpix cameras with the 28mm threads. Canon camcorders and a variety of other cameras
use the 28mm size. I had many of them made and still have quite a few left.
If you find you may need a quantity of the ones I have left just let me know and we can work something out.
These are brand new in plastic packaging and are very good quality.
received 6 Sept 2022
Extinction less complete than other linear polarizers; circular polarizer has more color that most;
1/4 wave plate alignment is presumably off.
Removing the (27mm o.d.) glass filter from 28mm mount was non-destructive and fairly easy.
27mm is a sloppy fit in Nikon vertical illuminator filter slots
quartz wedge appears to be from Leica, DIC condenser and nosepiece from Biophot